(a) Field of the Invention
The present invention relates to a process and equipment for preparing highly polymerized polycarbonate by polycondensation of polycarbonate prepolymers that are prepared by melt transesterification of carbonate ester and diol compounds using a horizontal tubular reactor comprising a plurality of rotating disks, a plurality of compartments divided by the rotating disks, and vents.
(b) Description of the Related Art
Highly polymerized polycarbonate is a widely used engineering plastic due to its high transparency, excellent thermal resistance and impact resistance.
Polycarbonate can be prepared by a Schotten-Baumann reaction. In this process, polycarbonate is prepared by interfacially polymerizing phosgene and diol compounds. However, since the reactant, phosgene, and the solvent, methylene chloride, used in said reaction are very toxic, the process involves many environmental problems.
In order to solve the above problems, a melt polymerization method was developed. Met polymerization is conveniently performed by the two steps of transesterification step and melt polycondensation step. In the melt transesterification step, carbonate ester and diol compounds are melt transesterified in the presence of a catalyst to prepare polycarbonate prepolymers, and in the melt polycondensation step, said prepolymers are transferred to a polymerization reactor and are polymerized further to obtain highly polymerized polycarbonates.
The following patents relate to the afore-mentioned polycondensation step, but they still involve some problems.
U.S. Pat. No. 5,384,389 discloses that a by-product, phenol, is removed by distillation after flowing polycarbonate prepolymer produced by transesterification in a molten state to a heated tubular reactor, and then inserting inert gas therein. However, it is difficult to remove phenol in a closed tubular reactor.
In addition, U.S. Pat. No. 5,589,564 discloses preparing polycarbonate by melt polymerization while flowing polycarbonate polymer down the wire strings, bound inside a vertical cylinder reactor regularly and vertically. However, it is difficult to obtain highly polymerized polycarbonate because the residence time is short.
According to the present invention, polycarbonate of a desired degree of polymerization can be obtained by polycondensation of polycarbonate prepolymer using a horizontal tubular reactor comprising rotating disks, a plurality of compartments divided by the rotating disks. The degree of polymerization of polycarbonate increases continuously when the reactant moves from one compartment to another compartment, and the residence time of the reactant can be controlled by controlling the feed rate of polycarbonate prepolymer. In addition, the final product is prevented from discoloration by discharging by-products, including aromatic alcohol, through the vents.